First: On your upgrade is a max level field. Modify that to 3.
Second: You'll need to modify what the upgrade does. You select the unit SCV, and you would scroll down until you find the units movement speed. To get the desired effect you would want to use a multiply operation.
Third: You need to properly setup requirements for the button to show up wherever you're upgrade is located. The two types of requirements are Use and Show. Use Requirements are the conditions that must be met to use the button. In other words the button will be greyed out if the conditions are not met. Show Requirements are the conditions that must be met for the button to actually show up on the unit, otherwise you won't even see the upgrade button.
Lastly: You need to setup the upgrade in a Research ability. Here you will setup the button icon, the requirement, time, cost etc, and the actual upgrade it self. It's helpful to name all of them the same name, preferably with a prefix so you know how to keep track of what is what.
Here is a link to an older post on how to do upgrades. I gave you the summary but this link should go in depth on how to accomplish what I just told you.
0.942634765061978